As shown in FIG. 1, it is known in the art to provide an on-line system 10 that produces a yarn or filament 20 from a process system 30. Process system 30 typically may include a continuous polymerization process and/or an extrusion melt process. Included within system 30 in FIG. 1 can be pre-polymer pumps and a reactor pump and/or an additive injection system with an extrusion booster pump. The spinning process portion of system 30 will also include a plurality of planetary/series pumps, extrusion heads, spin-finish pumps and spinerettes. The multi-filaments 20-1 output by a spinerette are combined to make yarn 20, which will be understood to include multiple filaments. Yarn 20 is provided to an input spool 40, to be collected on a take-up spool 50, which rotates in the direction shown. Yarn 20 may be perhaps 0.004" in diameter, and it may comprise dozens or hundreds of multi-filaments 20-1.
Extruded yarn material 20 can be processed for a variety of applications ranging from manufacturing, home furnishings (e.g., carpets, upholstery, drapes), apparel, and industrial yarns, depending upon the fineness of the yarn. "Denier" is a commonly used unit of fineness for yarn, and is equivalent to 1 g weight per 9 Km length of material. It is important to control quality and characteristics of the extruded yarn, including its denier.
Historically, larger denier yarn (e.g., perhaps 1,200 denier for carpet material) was manufactured with interlace nodes 60, produced along the length of the extruded material at intervals of perhaps 1 cm to 20 cm. The nodes were formed by causing the yarn to enter an air jet associated with a yarn end at a velocity exceeding the yarn exit velocity. The resultant bunching-up on the jet input side created compacted regions or nodes whose spaced-apart distances were a function of process parameters, especially yarn speed (perhaps 3 Km/min) and air jet pressure. These nodes prevented larger denier filament from unravelling during subsequent process, especially in a dry or static-electricity environment. More recently, nodes are also produced during fabrication of apparel class yarns as well, e.g., finer yarn in the range of a 100 denier or so. In apparel class yarns, the nodes are spaced-apart perhaps 1.2 cm to 2.5 cm or so.
As depicted in FIG. 1, it is not uncommon for produced yarn to have undesired broken segments or frayed portions 70. If such material is used to manufacture fabric, the imperfections adversely affect color dyeing as well as material consistency, for example because imperfect dye sites are present. Unfortunately such broken or frayed or even segments with missing strands have been relatively difficult to detect in the past, with resultant loss in yield of acceptable yarn produced.
Variations in denier, as well as changes in viscosity and/or density, can also affect color dyeing and consistency of material produced from a large number (perhaps a thousand) of packages of filaments that, ideally, would have identical characteristics. For example, the ability to extrude synthetic yarn is influenced by the flowability or viscosity of the material. Thus, a change in viscosity can manifest itself with changes in the crystalline structure of the material itself, including for example reorientation of the chain molecules within the material.
Material produced from filaments that have poorly controlled denier consistency, or viscosity or density characteristics, or excessive frayed and broken strands, may have to be discarded. Understandably discarding such material is a waste of time and resources, and degrades the effective yield of filament production. Further, many yarns undergo secondary manufacturing processes, such as draw texturing. It is important that the secondarily-processed material also be of consistent quality.
Conventionally, prior art systems 10 have attempted to measure denier by passing the extruded filament through a slotted capacitive bridge measuring system 80. For example, U.S. Pat. No. 3,879,660 to Piso discloses the use of a slotted balanced four-leg bridge capacitive sensor head system 80, in which the filament passed between the two plates of one of the capacitors. The bulk of the filament contributed a measurable charge imbalance as the filament passed through a somewhat large, e.g., about 10 mm.times.10 mm, effective window in the capacitive bridge. The sensor head output signals were analog, and the data acquisition signal processing circuitry coupled to the sensor head output signals made and processed perhaps ten measurements per second. The essentially analog denier measuring system was sensitive to electrical drift, especially due to changes in ambient temperature. Capacitive measurement systems are highly influenced by moisture in the yarn or measurement environment, which can degrade measurement reliability. Thus, such prior art systems could not readily be used to measure natural fibers, e.g., cotton, wool, flax, due to their high moisture content. Further, the effective measurement window was too large to sense frayed or broken strands 70, and no attempt was made to attempt to monitor nodes 60 in large denier filaments.
The '660 Piso system provided absolute denier measurements relative to a zero datum point that was obtained as a measurement with no filament present. The system provided calibration compensation such that the filament measurement output in the absence of any filament was forced to be zero denier. Unfortunately, contaminants from various sources could build-up between the capacitor plates, with the result that system 80 would eventually report too large a denier (due to bulk from contaminants) for a given filament size. The effective denier of the contaminants was perhaps 5 to 10, which meant that contamination drift could easily render apparel filament measurements grossly erroneous within a few days.
In addition, the system tended to exhibit signal drift and loss of absolute accuracy with respect to measured denier. Cleaning the sensor head to remove contaminants to restore signal accuracy meant taking the filament producing system off-line, perhaps every day or so. Although periodic sensor head cleaning improved measurement fidelity, production yield was reduced due to cleaning down-time, and quality of the material produced could suffer, prior to cleaning. At best, the '660 system could provide accurate measurements of denier, providing the analog system was maintained contaminant free and ambient temperature was controlled. No attempt to made to measure filament characteristics other than denier.
U.S. Pat. No. 4,208,625 to Piso disclosed an improved capacitive denier measuring system 80 with automatic calibration to compensate for sensor head drift. In addition to providing automatic zero compensation as in the '660 system, the 625 system provided automatic gain compensation gain. In essence, thermal gain drift was compensated by altering capacitive bridge excitation by a reference amount, and dynamically adjusting the system to produce a known corresponding change in the bridge output signal. Such gain compensation was done periodically, e.g., hourly, daily, or as frequently as seemed appropriate. (To further minimize thermal effects, the sensor head was maintained at about 50.degree. C.)
The normal filament-present measurement signal developed by the capacitive sensor head was combined with compensating signals representing zero gain and actual gain. The resultant automatic gain calibration meant that periodic system shutdowns for sensor head cleaning were not needed as often. While the '625 system represented improved denier measurement performance, this system was still analog in nature, and limited to about 10 measurements per second. As with the earlier system, the only filament characteristic measured was absolute denier. As a result, even if accurate denier measurements could be maintained for a period exceeding a few days, the resultant filament might still contain frayed or broken strands, viscosity changes, density changes, color changes, among other characteristic changes. However, even perfectly sized yarn that contained such changes could still result in a finished woven material that was defective, and would have to be rejected.
A somewhat different approach to denier-type measurement is disclosed in U.S.Pat. No. 5,099,504 (1992) to Pettit. Pettit '504 sensed yarn thickness by monitoring output from a particle radiation source, wherein the yarn to be measured was disposed between the source and an appropriate detector unit. While Pettit's device could provide a measure of denier and even density (providing the volume of the yarn was known), the device did not make meaningful use of optical properties of the yarn. Pettit's system does not respond to dye site defects, which can cause dying imperfections during fabrication with the yarn. Further, Pettit's device was expensive to fabricate (probably at least $1,000), cumbersome (probably at least 1 ft.sup.3) and exhibited some defects described earlier herein that characterize prior art approaches to denier and related yarn measurements.
In general, prior art systems have not been able to achieve DC stability better than 1 part per 1,000 to perhaps 1 part per 10,000. This DC stability parameter essentially affects measurement resolution, before any system drift occurs. Systems conventionally operate from perhaps 10V power supplies, and DC drift has limited Denier reading to perhaps 1% accuracy. Further, overall gain in prior art systems has been limited to perhaps 20,000 or less.
Prior art attempts to optically measure denier have long been plagued with the adverse effects of ambient conditions, including ambient light. For example, the room in which measurements are made will typically be illuminated with lights that will have a 60 Hz flicker component. This 60 Hz ambient light modulation will degrade optically based systems, and must somehow be accounted for.
In short, analog capacitive type denier measuring systems leave much to be desired, especially when fine apparel class yarns are to be monitored. Voltage gains in the prior art systems described typically was less than 5,000 or so, and signal to noise ratio did not permit greater than about 1 mV/denier. Capacitive based systems are also too susceptible to moisture, which can degrade measurement reliability. Particle radiation-based systems also leave much to be desired. Basically, prior art systems are blind to potential defects in the yarn or filaments being examined. Such defects include frayed, broken, or missing strands, changes in optical characteristics (e.g., viscosity, color, density). Other characteristic changes that could result in materials produced with the filaments being rejected after fabrication went similarly undetected in the prior art.
Thus there is a need for a rapidly executing high gain filament monitoring system that can measure absolute denier, denier spreads and variability, as well as monitor other filament parameters that affect quality control of the filament at the spinning level and/or the texturing level of production. Without limitation, such parameters should include optical characteristics, viscosity and density characteristics, interlace characteristics as well as dye sites and related structural changes that affect optical quality of the finished yarn. The system should operate on-line to detect defects including frayed or broken strands, missing or extra filaments, filament pump malfunction including jet contamination.
Such system should include automatic compensation for zero-denier and for gain, and feedback compensation for changes in the measurement medium. Further, such a system should enable on-line real-time monitoring of quality control production of the filament or yarn being produced and measurement results should not be substantially degraded by the presence of moisture. Preferably such measurements should be accurate within at least about .+-.1% and in applications ranging from spinning, spin drawing, spin draw texturing, draw texturing, and air jet texturing. The system should provide high but stable gain, low susceptibility to ambient lighting effects, and preferably should provide a resolution of perhaps 0.1 denier. Further, the system should provide a signal/noise ratio exceeding at least 20,000:1, and a sensitivity of at least 100 mV/denier.
The monitoring system should be substantially maintenance free, and be relative immune to the effects of contaminants and thermal drift. The monitoring system should not require frequent downtime of the yarn production system for maintenance. Finally, the system should be relatively inexpensive, uncomplicated to operate, and should be self-contained within a small package.
The present invention provides such a system.